1. Field of the Invention
The present invention relates to a liquid-droplet jetting apparatus which jets liquid droplets.
2. Description of the Related Art
As an ink-jet printer which jets an ink onto a recording paper or the like, there is known an ink-jet printer having an ink-jet head of line type (line-type ink-jet head) provided with a plurality of nozzles arranged in an array in a direction orthogonal to a feeding direction of the recording paper or the like. The line-type ink-jet head has an advantage that the line-type ink-jet head performs printing faster than an ink-jet head of serial type, because the line-type ink-jet head is capable of jetting ink from the nozzles arranged in a line entirely in the width of the recording paper to perform the printing. On the other hand, since the line-type ink-head has a large number of nozzles, when dust, air, and/or the like enter in any of the nozzles, jetting failure is easily occur such that the liquid droplet cannot be jetted (misfiring or non-discharge of liquid droplet); a liquid droplet of the ink is jetted in a direction deviated or bent from an intended direction (bending in the jetting direction), which in turn causes the liquid droplet land on a position deviated from an intended landing position; and the like. When such a jetting abnormality occurs, a while streak or line is formed in a recorded letter or image, and the like, thereby lowering the printing quality. To address this problem, there has been proposed an ink-jet head provided with an auxiliary head which jets the ink in place of a nozzle at which the jetting failure occurred, thereby degrading the printing quality.
For example, an ink-jet printer described in Japanese Patent Application Laid-open No. 2005-88417 is provided with a line-type ink-jet head and an auxiliary head (head for substituting recording or complementary recording) which is movable relative to the ink-jet head in a longitudinal direction of the ink-jet head (direction in which the nozzles are arranged). The auxiliary head has a plurality of nozzles arranged in one array in a direction in which the recording paper is fed (paper feeding direction). The ink-jet printer is constructed such that, when jetting failure occurs in any of the nozzles in the line-type ink-jet head, the auxiliary head is moved such that a nozzle among the nozzles in the auxiliary head is located at a position, which is same as that of the nozzle, at which the jetting failure occurs (failed nozzle), of the ink-jet head, with respect to the direction in which the nozzles of the ink-jet head and the nozzles of the auxiliary head are respectively arranged; and that the ink is jetted from the nozzle in the auxiliary head, thereby complementing (substituting for, compensating for) the failed nozzle in the ink-jet head.
As another example, an ink-jet printer described in Japanese Patent Application Laid-open No. 11-334047 is provided with a line-type ink-jet head as a primary head; and an auxiliary head which is also a line-type head, which is arranged side by side with the primary head in the feeding direction for recording paper and which has a construction identical to that of the primary head. The ink-jet printer is constructed such that, when jetting failure occurs in any of the nozzles in the primary head, the ink is jetted from a nozzle among the nozzles in the auxiliary head located at a position, which is same as that of the failed nozzle in the primary head, with respect to the direction in which the nozzles of the ink-jet head and the nozzles of the auxiliary head are arranged.
It should be noted, however, that the number of nozzles at which the jetting failure occurs is not always limited to one. For example, the jetting failure often occurs concurrently at not less than two nozzles when the ink, adhered to a liquid-droplet jetting surface of the ink-jet head, is sucked into not less than two nozzles adjacent to each other on the liquid-droplet jetting surface, resulting in air entering into these nozzles. In the auxiliary head described in Japanese Patent Application Laid-open No. 2005-88417, however, the nozzles in the auxiliary head are arranged in parallel in one array in the paper feeding direction. Therefore, this auxiliary head can complement only one nozzle in the ink-jet head at one jetting-execution position. Therefore, when the jetting failure occurs concurrently at a plurality of nozzles, it is necessary that the auxiliary head is moved frequently at positions each corresponding to one of the failed nozzles.
On the other hand, the auxiliary head described in Japanese Patent Application Laid-open No. 11-334047 is a line-type head. Accordingly, even when the jetting failure occurs concurrently at a plurality of nozzles in the primary head, the auxiliary head can complement these failed nozzles at one time. In this case, however, one ink-jet printer is required to have as many as two line-type heads each having a large number of nozzles, thereby substantially increasing the manufacturing cost of the printer as a whole.